Illumination system

ABSTRACT

The addition of DMD illumination modulator(s)  702  in series with projection SLM(s)  706/709  to produce high-performance projection displays with improved optical efficiency, reliability, and lower maintenance requirements. This approach eliminates the vibration, audible noise, and safety problems associated with high speed rotating color filter wheels  203  commonly used in SLM projectors and controls the light applied to individual areas of the projection SLM(s).

This application is a Divisional of application Ser. No. 10/186,734,filed 1 Jul. 2002 now U.S. Pat. No. 6,863,401 and issued 8 Mar. 2005 andProvisional Application No. 60/301,975, filed 30 Jun. 2001.

FIELD OF THE INVENTION

The present invention relates to spatial light modulator (SLM)projection displays and particularly to the illumination source in suchdisplays.

BACKGROUND OF THE INVENTION

In current SLM projection displays, such as DMD™ or LCD, the projector'slamp emits broadband (white) light, which is split into primary orsecondary color components by dichroic surfaces in stationary prisms,mirrors, or rotating panels, such as color wheels or drums. Thesefiltered planes of light are coupled to the projection SLM(s) insynchronization with pixelated image data. In the case of a DMDprojector, the projection DMD's mirrors are controlled by the image datato be either in the correct state for color projection to the screen orout of the field of view. Integrators are often added to homogenize theillumination.

DMD based projection displays typically use rotating color wheels, whichare optically inefficient, for color-plane separation. These colorwheels require motors, balanced parts, and rotary sensors all of whichcontribute negatively to system reliability, size, safety, noise,maintenance, and cost. The relative duty cycle of each color isconstant, determined by the relative dimensions of the filter panels. Bydesign, the filter panels only let specific wavelengths of light throughduring their working phase, therefore wasting the light of otherwiseuseful wavelengths.

Other projectors employ stationary color beam splitters that use two orthree defect-free SLMs to project distinct color plane images to thescreen. In these systems, two or three projection SLMs are opticallyconfigured in parallel to pixelate and relay the three-color imageplanes. Stationary beam splitting prisms have to be precisely aligned(converged) and stabilized to avoid image drift. The projection SLMsrequire even more precise alignment to prevent out-of-focus images andthese are position sensitive to thermal and structural stress.

While multiple projection SLMs in parallel have an advantage in opticalefficiency, negative factors are lifetime stability, mis-convergence,maintenance, MTBF, cost, and limited contrast due to light scatter fromthe constant, full area SLM illumination.

Projectors are configured using one SLM for lower cost systems, two SLMsfor higher performance systems, and three SLMs for very high brightnesssystems. All of these require very low defect projection SLM devices.

An example of a one-DMD projector with a rotating color wheelillumination system is shown in FIG. 1. In this case a light source,consisting of a lamp 100 and a collector 101, directs white light into afirst condenser lens 102, which brings the light down to a small focusedspot at the surface of a motor 104 driven rotating color filter wheel103. The light is segmented into sequential red-green-blue primarycolors by the color wheel and then resized to fit the DMD by a secondarycondenser lens 105, placed in the light path. Sometimes an optionalclear segment is added to the color wheel 103 for improved brightness.Light from this secondary condenser lens is focused on to the reflectivesurface of the DMD 106 where the micro-mirrors, which make up the matrixof pixels, are placed in binary states corresponding to the image datacontent, by the data path processor 107. Mirrors that are in the ONbinary state modulate and reflect sequential color images through aprojection lens 108 on to a viewing screen (not shown). The sequentialcolor images projected on the screen are integrated by the observer'seyes to provide a high quality color image. This type projector is lowercost since only one SLM is required and it offers auto-convergence sincethe color images are exactly laid on top of each other.

FIG. 2 a shows a typical configuration for a somewhat higher performanceDMD projection display, which used two projection DMD's and ayellow-magenta rotating color wheel. White light from a color source(lamp/collector) 200 is directed into a first condenser lens 202 by afirst turning mirror 201. This first condenser lens focuses the lightdown to a small spot at the surface of a motor 204 driven yellow-magentacolor wheel 203. Sequential red-green and red-blue light coming throughthe color wheel is then resized by a secondary condenser lens 205 andthen directed off the surface of a second turning mirror 206 into atotal-internal-reflective (TIR) prism 207, which is used to get lightinto and off of the two DMDs 209/210. Light from the TIR prism 207 iscoupled into a color splitting/recombining prism 208, where red light isreflected off an internal surface and focused on to the reflectivesurface of a first DMD 209 and sequential green-blue light is passedthrough the prism and focused on to the surface of a second DMD 210. Themicro-mirrors of the two DMD's are placed into their binary states basedon the image content by a data path processor 211. Red and green-bluelight is then modulated by the DMDs and reflected out of the recombiningprism 209, back through the TIR prism 207, and through a projection lens212 on to a viewing screen (not shown).

FIG. 2 b shows yet another even higher performance projection displayconfiguration, which also has two projection DMDs and a blue-greenrotating color wheel, but in this case the red light is split-off priorto the rotating color wheel. Here, white light from the source250/collector 251 is directed to a mirror 252, which reflects red lightalong a first path, through condensing optics (not shown) on to thereflective surface of a first DMD 253, and passes green-blue light intoa first condenser lens 254. This first condenser lens focuses thegreen-blue light down to a small spot at the surface of a motor 256driven rotating color filter wheel 255. Sequential green and blue lightcoming through the color wheel is then resized to fit a second DMD 256by means of a secondary condenser lens 258 and directed on to thesurface of the DMD 258. This sequential green-blue light is modulatedbased on the green-blue image content by data path processor 259 and thered light is modulated based on the red image content by data pathprocessor 260. The sequential green-blue modulated image and constantred modulated image are then combined by combining mirror 261 and thelight is directed through a projection lens 262 on to a viewing screen(not shown).

FIG. 3 shows a three-DMD projection display, which provides thehighest-performance, highest-brightness of those discussed. In this casethere is no rotating color wheel, but the system splits the white lightinto three constant red, blue, green beams going to respective DMDmodulators. Here, light from a white light source 300 is directedthrough a condenser lens 301 where it is sized and then turned by aturning mirror 302 and coupled into a TIR prism 303. The light isreflected off an internal surface of the TIR prism into a colorsplitting/recombining prism 304, where it is segmented into threecontinuous red, green, and blue beams, each being directed on to thereflective surface of a red 305, green 306, and blue 307 DMD. In eachcase the respective red, green, and blue light is modulated by the DMDmicro-mirrors, based on the respective image content, and the respectivecolor image is reflected back into the recombining prism 304. Therecombined superimposed red-green-blue images are then directed backthrough the TIR prism 303, through a projection lens 308 and on to aviewing screen 309. Of course, these images have to be perfectlyconverged (aligned) in the optics plane to provide a well-focusedpicture on the screen.

All of these displays have drawbacks resulting from either using therotating color wheel or from using an uncontrollable white light source.What is needed is a controllable light source that does not require theuse of a rotating color wheel. The illumination approach of the presentinvention meets this need in numerous embodiments by using additionalDMD illumination modulators to switch and control the light input to theprojection modulators. These illumination modulators can usually have acertain number of defects as compared to the projection modulators,thereby allowing reject devices to be used. Often times the illuminationmodulators can be smaller in size; i.e., can have fewer pixels. Inaddition, the illumination modulators can be used to control the amountof light going to certain areas of the projection modulators to lowerthe dark level and improve the contrast of the projected image, ascompared to using constant light levels in current systems. Thisapproach increases the contrast in one-SLM projection systems andimproves the optical efficiency in all DMD projection systems.

SUMMARY OF THE INVENTION

The present invention adds DMD illumination modulators in series withprojection SLM(s) to produce high-performance projection displays withimproved optical efficiency, reliability, and lower maintenancerequirements.

This approach eliminates the vibration, audible noise, and safetyproblems associated with high speed rotating color filter wheelscommonly used in SLM projectors. In addition, the DMD illuminationmodulators provide a means for controlling the light to each portion ofthe projection SLM(s), providing variable levels of each color toindividual pixels of the projection SLM. For example, color illuminationcan be directed only to those specific areas on the projection SLM whereit is needed, thus allowing lower dark levels and higher contrast forall images. Optimal coverage,.frequency, duration, and level of eachcolor can be provided to each projection SLM in order to at least doublethe optical efficiency of a projection system.

This solution increases contrast for all types of SLM projectors andincreases the optical efficiency for one-SLM and two-SLM projectionsystems. The increased light efficiency also enables the use of lowerpower lamps for a given output brightness, thereby increasing the lamplife and lowering the system cost.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic drawing of a conventional one-SLM projectiondisplay, which uses a rotating red-green-blue color filter wheel toprovide sequential red, green, and blue light to the projection SLM.

FIG. 2 a is a schematic drawing of a conventional two-SLM projectiondisplay, which uses a rotating yellow-magenta color filter wheel andcolor splitting/recombining optics to provide continuous red light toone projection SLM and sequential green and blue light to the otherprojection SLM.

FIG. 2 b is a schematic drawing of a conventional two-SLM projectiondisplay, which splits red light off to one SLM and uses a rotatinggreen-blue color filter wheel to provide sequential green and-blue lightto the other SLM.

FIG. 3 is a schematic drawing of a conventional three-SLM projectiondisplay, which uses a color splitting/recombining prism to provideuncontrolled, fixed red, green, and blue light to the respective SLMs.

FIG. 4 is a drawing illustrating the three operating states for a DMD;i.e., micro-mirrors tilted positive x degrees, tilted negative xdegrees, and tilted zero degrees (flat state).

FIG. 5 is a drawing illustrating the input and reflective output oflight for a DMD used with dark field optics.

FIG. 6 is a diagram illustrating the use of a single DMD illuminationdevice and dichroic mirrors to provide separable red and green-bluelight for use in two-SLM projection displays.

FIG. 7 is a schematic drawing for a first embodiment of the presentinvention, which uses a single illumination DMD in series with the twoparallel projection SLMs to implement an improved version of the systemof FIG. 2 a without a rotating color wheel.

FIG. 8 is a schematic drawings for a second embodiment of the presentinvention, which also uses a single illumination DMD in series withgreen-blue projection SLM, but splits off the red light and sends itdirectly to a dedicated red SLM to implement an improve version of thesystem of FIG. 2 b without a rotating color wheel.

FIG. 9 is a schematic diagram for a third embodiment of the presentinvention, which uses two illumination DMDs in series with twoprojection SLMs to implement an improve performance projection displaysystem without a rotating color wheel.

FIG. 10 is a schematic drawing for a fourth embodiment of the presentinvention, which uses a single illumination DMD in series with the threeparallel projection SLMs to implement an improved version of the systemof FIG. 3, but with controlled light properties for each of the threeSLMs.

FIG. 11 is a schematic diagram for a fifth embodiment of the presentinvention, which uses two illumination DMDs in series with a singleprojection SLM to implement an improve version of the system of FIG. 1without a rotating color wheel.

FIG. 12 is a schematic diagram for a sixth preferred embodiment of thepresent invention, which uses three illumination DMDs in series with asingle projection SLM to implement an improve version of the system ofFIG. 1 without a rotating color wheel.

FIG. 13 is a schematic diagram for a seventh embodiment of the presentinvention, which uses one or more illumination DMD with one or moreprojection SLM with emphasis on keeping all optical paths equal lengthin order to implement an improve version of the system of FIG. 1 withouta rotating color wheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention adds DMD illumination modulators in series withprojection SLM(s) to produce high-performance projection displays withimproved optical efficiency, reliability, and lower maintenancerequirements. This approach eliminates the vibration, audible noise, andsafety problems associated with high speed rotating color filter wheelscommonly used in SLM projectors. In addition, the DMD illuminationmodulators provide a means for controlling the light to each portion ofthe projection SLM(s), providing variable levels of each color toindividual pixels of each SLM.

Where lower cost, user-friendly projectors are required, such as in hometheater or consumer TVs, the present invention eliminates the need tomanually set convergence while being more power efficient than otherprojectors offering similar brightness. Concurrently, this inventionincreases contrast and greatly increases the optical efficiency ofsingle-SLM projection systems.

The invention is discussed in seven embodiments in the following text.

FIG. 4 is a drawing illustrating the three operating states for a DMD;i.e., (a) micro-mirror tilted zero degrees (flat state), (b) tiltedpositive x degrees, and (c) tilted negative x degrees. These states areall used to implement the various embodiments of the present invention.FIG. 4 a is a sketch of a DMD, which includes a substrate 400 with abuilt-in memory structure, and isolation layer 401 with interconnectvias covering the substrate, and a highly reflective micro-mirror 403attached to torsion hinges 402 on top of the isolation layer. Here themirror 403 is shown in the tri-state or flat condition. Incoming light404 that is perpendicular to the mirror surface is reflected 405straight back into the source, as shown.

FIG. 4 b illustrates the case where the micro-mirror 403 is tiltedpositive x degrees (typically +10°). The mirrors are tilted by applyingan electric field between the address electrodes and the mirrors, whichgenerates electrostatic forces that cause the mirrors to rotate on theiraxes. Depending on the binary state stored in the data content memorycell below each mirror, the rotational force is either positive ornegative. In this case, the incoming illumination 406 is perpendicularto the surface of the device and the reflected illumination 407 is +20°off axis from the input illumination.

Similarly in FIG. 4 c, the micro-mirror 403 is tilted negative x degrees(typically −10°). In this case, the incoming illumination 408 isperpendicular to the surface of the device and the reflectedillumination 409 is −20° off axis from the input illumination.

FIG. 5 illustrates another illumination case where the illumination DMDis used with dark field optics. This shows the substrate 500, isolationlayer 501, and a micro-mirror, attached to torsion hinges 502 (sideview), in the three states; i.e., rotated +x degrees 504, flat 506, androtated −x degrees 505. In this case, the illumination 503 comes in +20°off-axis from the surface of the device and reflects off themicro-mirror 90°, 70°, and 50° relative to surface of the device for the+x degree, flat, and −x degree states, respectively.

FIG. 6 is a diagram illustrating the use of a single DMD illuminationdevice and dichroic mirrors to provide separable red and green-bluelight for use in two-SLM projection displays. Here, white light 600 froma lamp is directed on to the surface of the illumination DMD 601 in themanner discussed in FIG. 4, with only the two binary states (+x and −xtilt angles) being used. Light coming off the illumination DMD in the +xdegree direction 603 is coupled to a yellow dichroic mirror 605 withred-green light being reflected off the dichroic. Likewise, light comingoff the illumination DMD in the −x degree direction 602 is coupled to amagenta dichroic mirror 604 with red-blue light being reflected off thedichroic. This red-green and red-blue light is then passed through a reddichroic 606 with the red light 607/608 being directed to the redprojection SLM 611 and the blue 609 and green 610 light beingsequentially directed to the blue-green projection SLM 612. Thisprovides a continuous red modulated image 613 and sequential blue andgreen images 614 to a projection lens without the use of a rotatingcolor wheel. The illumination DMD 601 can be used to completely controlthe light to individual areas of the projection SLMs.

FIGS. 7 a and 7 b are top and front views of a schematic drawing for afirst embodiment of the present invention, which uses a singleillumination DMD in series with the two parallel projection SLMs toimplement an improved version of the system of FIG. 2 a without arotating color wheel and using the yellow-magenta dichroic schemediscussed in FIG. 6. White light from a lamp 701 is collected by areflector 700 and directed on to the surface of an illumination DMD 702in a direction perpendicular to the surface of the DMD. Themicro-mirrors are sequentially switched between +x degrees and −xdegrees with light reflecting from the mirrors when tilted in the +xdirection 703 being reflected off a first turning mirror 704, through ared dichroic 705, on to the surface of a yellow dichroic 706. Lightreflecting from the mirror when tilted in the −x direction 707 isreflected off a second turning mirror 708, through the red dichroic 705,on to the surface of a magenta dichroic 709. The red-green lightreflected off the yellow dichroic 706 is split apart by the red dichroic705 with the red light being reflected on to the surface of a dedicatedred projection SLM 711 and the green light being directed through thered dichroic on to the surface of a blue-green projection SLM 710.Likewise, the red-blue light reflected off the magenta dichroic 709 isalso split apart by the red dichroic 705 with the red light beingreflected on to the surface of the dedicated red projection SLM 711 andthe blue light being directed through the red dichroic on to the surfaceof the blue-green projection SLM 710. Finally, the continuous redmodulated image 712 from the dedicated red projection SLM 711 and thesequential blue-green image 713 from the blue-green projection SLM 710are reflected into the aperture of a projection lens 714 for focusing ona viewing screen (not shown).

The approach of the present invention eliminates certain artifactsassociated with rotating color wheels by adjusting the frequency andduration of each color separation DMD pixel. Variable levels of eachcolor can be transmitted to each pixel from 0–100% of the availableenergy for a particular color. Color illumination can be directed onlyto those specific areas on the projection SLM where it is needed, thusattaining optimal dark level conditions and thereby improved contrastfor all images. Optimum coverage, frequency, duration, and level ofcolor light exposure at each projection SLM pixel can be maintained.

Optical efficiency (ratio of lumens input over lumens output) for aconventional single projection DMD projector with color wheel istypically 10%. The use of the DMD color filter illumination method ofthe present invention can double this efficiency to 20% in manyapplications.

Also, it is not necessary that the illumination DMD have the same numberof pixels as the projection SLM and the illumination DMD can have acertain number of defects (inoperable micro-mirrors) depending on theapplication. This allows the rotating color wheel to be replaced by anassembly that uses reject DMD(s).

FIG. 8 is a schematic drawing for a second embodiment of the presentinvention, which also uses a single illumination DMD in series withgreen-blue projection SLM, but splits off the red light and send itdirectly to a dedicated red SLM to implement an improve version of thesystem of FIG. 2 b without a rotating color wheel. White light from alamp 801 is collected by reflector 800 and directed into a first TIRprism 802 where the red light is reflected off an internal surface intoa second TIR prism 803. Here, the red light is again reflected off aninternal surface on to the reflective surface of the red SLM 804, whereit is modulated based on the red image data content and reflected fromthe ON pixels of the SLM back through the second TIR prism 803 into aprojection lens 805. In parallel, cyan light passes through the firstTIR prism 802 on to the micro-mirrors of an illumination DMD 806 along apath that is perpendicular to the surface of the DMD. The micro-mirrorsof the illumination DMD 806 sequentially switch between +x degrees and−x degrees with light reflecting from the mirrors when tilted in the +xdirection 807 being reflected off a first turning mirror 808, through afirst lens with an integrator or diffuser 809, on to the surface of ablue dichroic 810. Light reflecting from the mirrors when tilted in the−x direction 812 is reflected off a second turning mirror 813, through asecond lens with an integrator or diffuser 814, on to the surface of agreen dichroic 815. The blue light reflected off the blue dichroic 810is then sequentially reflected on to the surface of a projectionblue-green SLM 811. Likewise, the green light reflected off the greendichroic 815 is also sequentially reflected on to the surface of theblue-green projection SLM 811. Finally, the sequential blue-green lightis sequentially modulated based on the data content of the blue andgreen images, respectively, and sequentially reflected from theblue-green projection SLM 811 into the aperture of a second projectionlens 816 for focusing the image on a viewing screen. Optionally, asingle projection lens can be used, but in either case the red andblue-green images must be converged for a well-focused image. However,in this arrangement the convergence occurs at the much larger screendimensions compared to typical alignment in the optics plane.

FIG. 9 is a schematic drawing for a third embodiment of the presentinvention, which uses two illumination DMDs in series with twoprojection SLMs to implement an improve performance projection displaysystem without a rotating color wheel. In this configuration, whitelight from a light source (not shown) is passed through a first turningmirror 900 onto the surface of a yellow dichroic 901 from which yellow(red-green) light is reflected into a first yellow illumination DMD 902and magenta (red-blue) light is passed through on to the surface of asecond magenta illumination DMD 903. The yellow and magenta light isrespectively modulated to optimally control the system performance bymeans of these two illumination DMDs. Modulated light from the yellowillumination DMD 902 is reflected off the ON micro-mirrors back on tothe yellow dichroic 901. This light is then reflected off the yellowdichroic 901, off the reflective surface of the first turning mirror900, off the reflective surface of a second turning mirror 904, througha red dichroic 905, on to the reflective surface of a blue-green SLM906. Similarly, the modulated light from the magenta illumination DMD903 is passed back through the yellow dichroic 901, off the reflectivesurface of the first turning mirror 900, off the reflective surface ofthe second turning mirror 904, off the surface of the red dichroic 905,on to the reflective surface of a red SLM 907. A modulated red image isthen reflected from the ON pixels of the red SLM 907, off the reddichroic 905, and into a projection lens (not shown). Likewise,sequential modulated blue and green images are reflected from the ONpixels of the blue-green SLM 906, through the red dichroic 905, into theprojection lens. In operation, by turning the yellow illuminator 902 andmagenta illuminator 903 ON and OFF out of phase with an optimized dutycycle and then filtering the light as discussed above, sequentialblue-green light is provided to the blue-green SLM 906 and continuousred light is provided to the red SLM 907.

FIG. 10 is a schematic drawing for a fourth embodiment of the presentinvention, which uses a single illumination DMD in series with the threeparallel projection SLMs to implement an improved version of the systemof FIG. 3, but with controlled light properties for each of the threeSLMs. In this embodiment, white light is directed into a TIR prism 1001where it is reflected off a first internal surface on to the reflectivesurface of an illumination DMD 1002. Controlled light from thisillumination DMD is reflected off the chip's micro-mirrors, through theTIR prism 1001, into a color splitting/recombining prism 1003, where itis broken into the three primary beams and directed to dedicated red,green, and blue SLMs 1004–1006, respectively. The three (red, green, andblue) modulated color images are then reflected off the respective SLMsand recombined in the recombining prism 1003 and directed back into theTIR prism 1001, where it is reflected off a second internal surface intoa projection lens 1007.

In operation, the TIR prism 1001 is used to get light into and out ofcolor splitting/recombining prism 1003. Since there is no color wheelinvolved in the conventional version of the system, as illustrated inFIG. 3, the illumination DMD 1002 is used solely to control the light todifferent portions of the three SLMs 1004–1006.

FIG. 11 is a schematic drawing for a fifth embodiment of the presentinvention, which uses two illumination DMDs in series with a singleprojection SLM to implement an improved version of the system of FIG. 1without a rotating color wheel. In this embodiment, white light 1110 isdirected into an input TIR prism 1102, where red light is reflected offan internal surface on to the surface of a red illumination DMD 1101 andblue-green light passes through the input TIR prism on to the surface ofa blue-green illumination DMD 1100. Since this configuration is for asingle-chip SLM projector, the applied light needs to be sequentialred-green-blue. Therefore, the red illumination DMD 1101 is turned ON(micro-mirrors tilted +x degrees) for a portion of the field and OFF(micro-mirrors tilted −x degrees) for the remainder of the field whengreen or blue light is being supplied. On the other hand, themicro-mirrors of the green-blue DMD 1100 are placed in one binaryposition (say +x degrees) to supply green light and in the other binaryposition (−x degrees) to supply blue light. During the time that redlight is being supplied, the green-blue DMD 1100 is placed in thetri-state (flat) position, as described in FIG. 4 a. This mode ofoperation provides the necessary sequential red-green-blue illuminationto the projection SLMs. The red light is modulated (controlled) by thered illumination DMD 1101 and reflected back into the input TIR prism1102 where it is reflected off an internal surface. Similarly, the greenand blue light is modulated by the green-blue illumination DMD 1100 andalso passed back through the input TIR prism 1102. Then this availablesequential red-green-blue controlled light is supplied to the input ofan optical triplet 1103–1105, consisting of an input concave lens 1104,a yellow-magenta dichroic section 1103, and an output concave lens 1105.When green light is available from illumination DMD 1100, it is benttowards a yellow dichroic 1106 where it is reflected back through theoutput concave lens 1105, in order to straighten out its path, throughan output TIR prism 1108, on to the surface of the single projection SLM1109. The output TIR prism 1108 is used to get the light on to and offof the projection SLM 1109. Likewise, when blue light is available fromillumination DMD 1100, it is bent towards a magenta dichroic 1107 whereit is reflected back through the output concave lens 1105, through theoutput TIR prism 1108, on to the surface of the single projection SLM1109. Again, during the time that green and blue light is being suppliedthe red illumination DMD 1101 is turned OFF. To supply red light, firstthe green-blue illumination DMD 1100 is put in the tri-state (flat)position and the red illumination DMD 1101 is turned to the ON binarystate. Depending on which binary state is chosen as the ON state, thered light will follow the path of either the green or blue light throughthe triplet 1103–1105 and on to the surface of the projection SLM; e.g.,the green path leading to the yellow dichroic 1106 is shown in thedrawing. Finally, the sequential red, green, and blue images aremodulated by the projection SLM, according to the image's color planecontent, and reflected off the reflective surface back through theoutput TIR prism 1108 into a projection lens (not shown).

Not only does this embodiment provide complete control of the light toindividual pixels on the projection SLM 1109, but the output TIR prism1108 establish correct working distances and enables separation of adesirable f/3 optical input cone from the DMDs output cone.

Table 1 shows the states for this two illumination DMD approach, whichutilizes the two binary states and the tri-state of the two illuminationDMD's 1100/1101.

TABLE 1 R B/G RED ON TRI-STATE GREEN OFF G BLUE OFF B

FIG. 12 is a schematic drawing for a sixth preferred embodiment of thepresent invention, which uses three illumination DMDs in series with asingle projection SLM to implement an improve version of the system ofFIG. 1 without a rotating color wheel. Here, three-beam splitters forred, green, and blue chroma are in series with three-color separationillumination DMDs. This approach offers fully addressable rays of singlecolor, such as red, green, and blue for a single-SLM system, or yellowand magenta for a two-SLM system. These modulated, fully addressablerays allow for sized bundles of color illumination to be transmitted tospecific areas on the defect free projection SLM(s). In this case, whitelight 1200 is supplied to an input/output TIR prism 1201, used toseparate the incoming and outgoing illumination, where it is reflectedoff an internal surface and directed into a color splitting/recombiningprism 1202. The light is split into three primary beams (red, green, andblue) and directed by the prism to respective red 1203, green 1204, andblue 1205 illumination DMDs. These DMDs are turned ON and OFFsequentially, modulating the light for optimal projector performance andreflecting the sequential red-green-blue light beam back through therecombining prism 1202, keeping the color images converged, and backthrough the input/output TIR prism 1201, on to the reflective surface ofthe projection SLM 1206. The projection SLM then sequentially modulatesthe color images according to the color image content and reflects themback input the TIR prism 1201 where they are reflected off an internalsurface through a projection lens 1208 on to a viewing screen (notshown). This is the high-end approach to replacing the color wheel in asingle-SLM projector with illumination DMDs since individual DMDs areused to control each of the three primary color planes. One examplewould be to use the illumination DMDs 1203–1205 to remove the light inareas of the SLM 1206 where it should be dark in order to improve thecontrast of the projected image.

FIG. 13 is a schematic diagram for a seventh embodiment of the presentinvention, which uses one or more illumination DMDs with one or moreprojection SLMs with emphasis on keeping all optical paths equal lengthin order to implement an improve version of the system of FIG. 1 withouta rotating color wheel. In this generic embodiment, one, two, or threeillumination DMDs 1300 are used with one, two, or three projection SLMs1308 to provide an optimal performance projection system with fastswitching and controllable illumination. White light is directed into ainput TIR prism 1301, where it is reflected off an internal surface andon to the surface of the illumination DMD(s) 1300. Controlled light fromthese DMDs is reflected back through the TIR prism 1301 along two paths1302/1303, on to additional TIR surfaces or mirrors 1304/1305, throughan output TIR prism 1307, to the respective projection SLM(s) 1308.These SLM(s) then modulates the images according to color and gray levelcontent, and then reflects them back through the output TIR prism 1307to a projection lens. Optional diffusers, diffraction gratings, orintegrating elements 1309/1310 can be added in the input and outputpaths for additional optical optimization. In the case where theillumination DMDs have stuck-on or stuck-off pixels, these diffusers,diffraction gratings, or integrating elements can mask the defectswithout negative effects on the viewing screen.

In some configurations, it is permissible for the illumination DMDs tomodulate specific areas of illumination so that an integrator is notrequired to provide uniform illumination. Also, the placement order ofthe various lenses, integrators, diffusers, and dichroic surfaces(mirrors and prisms) before or after the illumination DMDs and/orprojection SLMs is a system design issue for which many options areavailable.

In a system where multiple color separation illumination DMD(s) are usedin series with the projection SLM(s) to separate, then gate the colorrays to the viewing screen, electronic convergence of the colorseparation DMD(s) can be enabled with appropriately designed testtargets. The modulation frequency and duration of the color separationDMD(s) may be synchronized with the projection SLM(s) and adjusted inreal-time to varying image requirements. It may also be desirable tocontrol the relative timing of the DMDs to mask other image defects orscreen properties. Digital Signal Processors (DSPs) may be employed toprocess time critical data for these and other image adjustments.

The illumination can be dimensionally adjusted electronically toaccommodate various image display formats such as 4:3, 16:9, letterbox,and future High Definition TV standards. Additional optics, such asanamorphic lenses or diffraction gratings may be used to redistributethe illumination to the aspect ratio desired on the viewing screen.

In these projectors, the color separation DMDs can often be placed inthe assembly without precision alignment or convergence mechanisms andthe associated labor. Instead, automated cameras and electronic controlscan be used to verify the x, y, z, and theta illumination alignment atthe projector output. The illumination pattern for each color isadjusted by addressing the appropriate mirrors on each color separation(illumination) DMD, corresponding to the image pattern from theprojection SLM. When a test pattern is the brightest and most uniform asdetected by the camera (or technician), the illumination rays of eachillumination DMD are correctly mapped (converged) to the projection SLM.If required, the illumination pattern can be scaled as well, in terms ofoverall size or individual pixel coverage. In the latter case, more orless illumination DMD pixels are assigned to the projection SLM pixels,thereby maximizing the dark levels at the viewing screen.

While the present invention has been described in the context of severalembodiments, it will be apparent to those skilled in the art that theinvention may be modified in numerous ways and may assume embodimentsother than that specifically set out and described above. Accordingly,it is intended by the appended claims to cover all modifications of theinvention that fall within the true spirit and scope of the invention.

1. A display, comprising: at least one illumination modulator comprisingan array of elements operable in a first state directing incident lightalong a first path, and a second state directing incident light along asecond path; a first color filter on said first path for directing afirst filtered light beam to at least one spatial light modulator; asecond color filter on said second path for directing a second filteredlight beam to said at least one spatial light modulator; and said atleast one spatial light modulator for spatially modulating said firstand second filtered light beams to form an image-bearing light beam. 2.The display of claim 1, wherein at least one of said first color filterand said second color filter is a dichroic filter.
 3. The display ofclaim 1, wherein at least one of said first color filter and said secondcolor filter is a diffraction grating filter.
 4. The display of claim 1,wherein at least one of said first color filter and said second colorfilter is a secondary color filter.
 5. The display of claim 1, whereinsaid first color filter and said second color filter are a yellow and amagenta color filter.
 6. The display of claim 1, comprising a prismassembly directing said filtered light to said at least one spatiallight modulator.
 7. The display of claim 1, at least one of said atleast one illumination modulator and said at least one spatial lightmodulator comprising a micromirror device.
 8. The display of claim 1,said at least one spatial light modulator comprising three micromirrordevices.
 9. The display of claim 1, comprising a color splitter toseparate said first and second filtered light beams into separate colorlight beams.
 10. The display of claim 1, comprising a color splitter toseparate said first and second filtered light beams into three separatecolor light beams directed along three light paths, said at least onespatial light modulator comprising a spatial light modulator on each ofsaid three light paths.
 11. The display of claim 1, comprising: a lightsource for producing a beam of light along an illumination path to saidat least one illumination modulator; a color filter on at least one ofsaid illumination path, said first path, and said second path fordirecting a portion of light along a separate color light path; and aseparate color spatial light modulator on said separate color light pathfor spatially modulating said portion of light.
 12. A display,comprising: at least one illumination modulator on a first light path,said at least one illumination modulator comprising an array of elementsoperable in a first state directing incident light along a first path,and a second state directing incident light along a second path; a firstcolor filter on said first path for directing a first filtered lightbeam to at least one spatial light modulator; a second color filter onsaid second path for directing a second filtered light beam to said atleast one spatial light modulator; said at least one spatial lightmodulator spatially modulating said first and second filtered lightbeams to form an image-bearing light beam; and wherein at least one ofsaid first color filter and said second color filter is a diffractiongrating filter.
 13. A display, comprising: a light source for producinga beam of light along an illumination path; at least one illuminationmodulator on said illumination path, said at least one illuminationmodulator comprising an array of elements operable in a first statedirecting incident light along a first path, and a second statedirecting incident light along a second path; a first color filter onsaid first path for directing a first filtered light beam to at leastone spatial light modulator; a second color filter on said second pathfor directing a second filtered light beam to said at least one spatiallight modulator; a third color filter on at least one of saidillumination path, said first path, and said second path for directing aportion of light along a separate color light path; a separate colorspatial light modulator on said separate color light path for spatiallymodulating said portion of light; and said at least one spatial lightmodulator for spatially modulating said first and second filtered lightbeams to form an image-bearing light beam.
 14. The display of claim 13,wherein at least one of said first color filter, said second colorfilter, and said third color filter is a dichroic filter.
 15. Thedisplay of claim 13, wherein at least one of said first color filter,said second color filter, and said third color filter is a diffractiongrating filter.
 16. The display of claim 13, wherein at least one ofsaid first color filter, said second color filter, and said third colorfilter is a secondary color filter.
 17. The display of claim 13, atleast one of said at least one illumination modulator, said spatiallight modulator, and said separate color spatial light modulatorcomprising a micromirror device.